For example, a conventional pulverized-coal-combustion boiler includes a furnace which is formed in a hollow shape and is provided in the vertical direction, and plural combustion burners are disposed in a furnace wall in the circumferential direction and are disposed at plural stages in the up and down direction. A fuel-air mixture obtained by mixing primary air with pulverized coal (fuel) formed by milling coal is supplied to the combustion burners, and hot secondary air is supplied to the combustion furnaces so that the fuel-air mixture and the secondary air blow into the furnace. Accordingly, a flame is generated, and hence the fuel-air mixture may be burned inside the furnace by the flame. Then, a flue gas duct is connected to the upper portion of the furnace, and the flue gas duct is equipped with a superheater, a repeater, an economizer, and the like for collecting the heat of a flue gas. Thus, steam may be produced by the heat exchange between water and the flue gas produced by the combustion in the furnace.
As such a pulverized-coal-combustion boiler or such a combustion burner, for example, pulverized-coal-combustion boilers or combustion burners disclosed in Patent Literatures below are known.